Need to rewrite C++ code to PHP

Question

I have a task. I need to rewrite C++ code to PHP.

#include <iostream>
using namespace std;

struct Structure {
    int x;
};

void f(Structure st, Structure& r_st, int a[], int n) {
    st.x++;
    r_st.x++;
    a[0]++;
    n++;
}

int main(int argc, const char * argv[]) {

    Structure ss0 = {0};
    Structure ss1 = {1};
    int ia[] = {0};
    int m = 0;
    f(ss0, ss1, ia, m);
    cout << ss0.x << " "
         << ss1.x << " "
         << ia[0] << " "
         << m     << endl;

    return 0;
}

return of a compiler is 0 2 1 0. I have rewrote this code in PHP like this:

<?php

class Structure {
    public function __construct($x) {
        $this->x = $x;
    }

    public $x;
}

function f($st, $r_st, $a, $n) {
    $st->x++;
    $r_st->x++;
    $a[0]++;
    $n++;
}

$ss0 = new Structure(0);
$ss1 = new Structure(1);

$ia = [0];
$m = 0;

f($ss0, $ss1, $ia, $m);
echo $ss0->x    . " "
     . $ss1->x  . " "
     . $ia[0]   . " "
     . $m       . "\n";

return of this code is: 1 2 0 0. I know PHP and I know why it is returning this values. I need to understand how in C++ struct works and why a[0]++ is globally incremented. Please help to rewrite this code on PHP. I also know than there is no struct in PHP.

int a[] is the same as int* a, so the parameter is passed as a pointer. a[0]++ increments the object pointed to, not a local copy. — Bo Persson
– Bo Persson, Commented Dec 1, 2016 at 15:12
Also note that the only difference between a class and a struct in C++ is default access for its members. — Cinder Biscuits
– Cinder Biscuits, Commented Dec 1, 2016 at 15:20
Struct is same as Class. The only difference is all properties & methods in struct is always public by default. a[0]++ is globally incremented because you pass an array of pointer not a copy of array. For understanding this you can learn array of pointer from google. — Nazmul Hasan
– Nazmul Hasan, Commented Dec 1, 2016 at 15:54

Starl1ght · Accepted Answer · 2016-12-01 15:18:48Z

Difference between:

function f($st, $r_st, $a, $n)
void f(Structure st, Structure& r_st, int a[], int n)

in C++ you always specify, pass by value or by reference, but in PHP there are some pre-defined rules.

Fix for 1st output

C++ part: st is passed by value, and original value, which you pass here is not changed. r_st is passed by reference, and original value is changed.

PHP part: both arguments are passed by reference, since they are classes.

Simple fix there is to clone object st and pass it to function to mimic C++ pass-by-copy, or clone it inside function.

Fix for 3rd output

in C++ int a[] is passed as pointer, so, original value is changed, but in PHP it is passed by value, and it is unchanged outside.

Simple fix for it would be &$a instead of $a in function parameters.

PS. I'm C++ developer, so, PHP part can be inaccurate in terminology.

Kevin Stich · Accepted Answer · 2016-12-01 15:11:20Z

1

The ss0 and ss1 variables you are passing in are by object accessors to that function. See Objects and references

The variables passed in are by value. See Passing by Reference

answered Dec 1, 2016 at 15:11

Kevin Stich

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Comments

JustOnUnderMillions · Accepted Answer · 2016-12-01 15:16:51Z

0

Please help to rewrite this code on PHP.

Do it like this

function f($st, $r_st, &$a, $n) {

     $st= clone $st; #clone to get a real copy, not a refer

     $st->x++;
     $r_st->x++;
     $a[0]++; #&$a to simulate  ia[] (use as reference)
     $n++;
}

Read about references in PHP. I'm not a C++ dev.

http://php.net/manual/en/language.oop5.cloning.php

edited Dec 1, 2016 at 15:16

answered Dec 1, 2016 at 15:11

JustOnUnderMillions

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